The present invention generally relates to anode devices used to inhibit corrosion in metal water heater tanks and other metal liquid storage vessels and, in a preferred embodiment thereof, more particularly relates to a specially designed resistored anode assembly useful in this corrosion-inhibiting application.
Conventional metal water heater tanks, like other types of metal vessels used to store liquids, are subject to corrosion during use. To inhibit this corrosion, sacrificial anodes, normally constructed of magnesium, aluminum or zinc, are inserted into the tank. The sacrificial anode is slowly consumed during the corrosion protection process while generating an electrical current. AS the anode is slowly depleted, its simultaneously generated electrical current catholically protects the tank against corrosion.
The service life of the anode tends to be inversely dependent upon the amount of electrical current it generates in cathodically protecting the tank. In many fresh water supplies, particularly those having a high mineral content, the current flow generated by the anode is relatively high, resulting in a corresponding decrease in the useful life of the anode. In order to control the rate of consumption of a sacrificial anode, various anode constructions have been previously proposed in which a resistor is incorporated in the anode, and electrically connected between the anode and its protected tank, to automatically regulate the electrical current generated by the anode during its operation and thereby increase the service life of the anode.
While these resistored anode devices typically extended anode life, many of them also tended to be of a relatively complex construction, rather difficult to assemble, and relatively expensive to fabricate.
Many of these problems were essentially eliminated by a prior art sacrificial anode assembly that incorporated, in a simplified manner, an ordinary barrel-type carbon resistor into the interior of the assembly. This prior art anode assembly included a cylindrical plastic insulating sleeve captively retained within a metal cap portion of the anode assembly and having a closed end with a central opening through which an end portion of the metal anode body core rod extended. A diametrically extending groove, which intersected the central sleeve opening, was formed in the closed sleeve end.
The cylindrical resistor body was disposed in a radial portion of the sleeve end groove, with one of the resistor end leads being radially extended over the anode rod end and soldered or welded thereto. The other resistor end surface groove in the insulating sleeve end passed through an axially extending exterior side surface groove in the insulating sleeve and was soldered or welded at its outer end to an external metal cap portion of the anode assembly.
Although this method of operatively positioning a resistor in a sacrificial anode assembly provided a worthwhile reduction in assembly time and cost, and provided the desired regulation of anode current generation, it was found that it could create a problem relating to the structural integrity of the completed anode assembly. Specifically, it was found that in certain shipping orientations of the tank in which the anode assembly was installed, harmonic vibration might be created within the central anode core rod which were transmitted to the solder or weld joint connecting a resistor end lead to the rod. These vibrations could fatigue and break the rod/lead solder or weld joint, thereby rendering the anode assembly inoperative.
This vibration-created breakage of the rod/lead solder or weld joint was substantially eliminated by the anode assembly improvements incorporated in this type of anode assembly as illustrated and described in U.S. Pat. Nos. 5,256,267 and 5,334,299, each of such patents having been assigned to the assignee of the present invention. Such patents are hereby incorporated by reference herein in their entireties. The improvements illustrated and described in these patents comprise replacing the axial cap end groove with a generally U-shaped surface groove, forming a generally U-shaped bend in the resistor lead to be soldered to the anode core rod, placing the U-shaped bend portion of the resistor lead into the U-shaped surface groove, and then soldering or welding the outer end of the resistor lead to the anode core rod. This configuration and placement of the soldered or welded resistor lead extending along the closed plastic sleeve end provided the lead with a flexure capability that substantially eliminated vibration-caused breakage thereof at the lead/rod solder or weld joint.
However, a problem with this constructional approach was subsequently discovered. Specifically, during electrically conductive connection of the resistor lead to the anode rod (as by soldering or welding) the lead could be forcibly engaged with the bottom side of its associated sleeve groove and deflected outwardly therefrom in a manner such that when the sleeve was subsequently pressed into the metal cap of the overall anode assembly, the deflected lead could contact and electrically short out against the metal cap.
A means to prevent this undesirable electrically shorting effect was implemented by the manufacturer of the anode assembly by using a drop of an ultra violet light-cured adhesive onto the lead and the plastic sleeve. This gave a firm immediate bond of the lead wire to the plastic sleeve, thereby preventing movement of the lead wire during the lead wire/anode rod welding or soldering process. Examination of field failures indicated that this corrective procedure reintroduced the stress on the lead wire that had previously been relieved by the generally U-shaped bend in the lead wire. If there was any movement of the sleeve on the anode or movement of the anode within the sleeve, a substantial stress was placed on the lead wire adjacent the lead wire/anode rod weld or solder joint. This same phenomenon was encountered if the plastic sleeve absorbed water causing the plastic to swell in a manner forcibly moving the lead wire and causing breakage thereof, thereby rendering the anode assembly ineffective in providing corrosion to its associated tank.
As can be seen from the foregoing, a need exists for a solution to these constructional problems presented in a protective anode assembly of the type described above. It is to this need that the present invention is directed.